The United States has begun launching drone strikes against suspected al-Qaeda operatives in Yemen under new authority approved by President Obama that allows the CIA and the military to fire even when the identity of those who could be killed is not known, U.S. officials said.

The policy shift marks a significant expansion of the clandestine drone war against an al-Qaeda affiliate that has seized large ­pieces of territory in Yemen and is linked to a series of terrorist plots against the United States.

U.S. officials said that Obama approved the use of “signature” strikes this month and that the killing of an al-Qaeda operative near the border of Yemen’s Marib province this week was among the first attacks carried out under the new authority.

The decision to give the CIA and the U.S. Joint Special Operations Command (JSOC) greater leeway is almost certain to escalate a drone campaign that has accelerated significantly this year, with at least nine strikes in under four months. The number is about equal to the sum of airstrikes all last year.